Method for levitation control of a linear motor, method for measuring a position of a linear motor, inductive sensing device, and elevator system

Abstract

A method for levitation control of a linear motor includes supplying an alternating current or alternating voltage to at least one oscillating circuit including at least one sensing coil being or assumed to be arranged in a fixed spatial correlation to a mover part of the linear motor such that an opening plane of the sensing coil faces a sensor counter-surface of a stator part of the linear motor with a gap therebetween; receiving a response signal from the oscillating circuit; determining a gap length of the gap based on the response signal; and controlling the gap length by driving a magnetic levitation unit of the linear motor based on the determined gap length. An inductive sensing device and an elevator system, and a method for determining a position of the linear motor are also disclosed.

The invention claimed is: 
     
       1. A method for levitation control of a linear motor, comprising the steps of:
 supplying an alternating current or alternating voltage to at least one oscillating circuit comprising at least one sensing coil arranged in a fixed spatial correlation to a mover part of the linear motor such that an opening plane of the sensing coil faces a sensor counter-surface of a stator part of the linear motor with a gap therebetween; 
 receiving a response signal from the oscillating circuit; 
 determining a gap length of the gap based on the response signal; and 
 controlling the gap length by driving a magnetic levitation unit of the linear motor based on the determined gap length. 
 
     
     
       2. The method of  claim 1 , wherein the supply of alternating current or alternating voltage is controlled to maintain an oscillation amplitude of the oscillation circuit at a constant level while monitoring the energy consumption, and the gap length is determined based on a variation of the monitored energy consumption, wherein the response signal corresponds to the monitored energy consumption. 
     
     
       3. The method of  claim 1 , wherein the alternating current or alternating voltage is generated with a stable reference frequency while monitoring the oscillation frequency of the oscillation circuit, and the gap length is determined based on a deviation of the monitored oscillation frequency from the reference frequency, wherein the response signal corresponds to the monitored oscillation frequency. 
     
     
       4. The method of  claim 1 , wherein the alternating voltage is supplied with a constant amplitude while monitoring an amplitude of a responsive alternating current generated in the oscillation circuit in response to the supplied alternating voltage; then a frequency of the alternating voltage is changed gradually such that the amplitude of the responsive alternating current changes towards a preset reference current value until the amplitude of the responsive alternating current corresponds to the reference current value; then a frequency of the alternating voltage that causes this current is detected and is compared to a preset reference frequency value; and the gap length is determined based on a difference of the detected frequency from the reference frequency value, wherein the response signal corresponds to the frequency of the alternating voltage. 
     
     
       5. The method of  claim 1 , wherein the method is executed using an inductance-to-digital converter having a conversion rate of 5 ksps or more. 
     
     
       6. The method of  claim 1 , wherein the response signal is used for determining a position and/or velocity and/or acceleration of the mover part with respect to the stator part in a moving direction of the mover part, based on the stator part where the sensor counter-surface is formed having alternating electric conductivity and/or magnetic permeability properties in a moving direction of the mover part. 
     
     
       7. The method of  claim 6 , wherein an amplitude or change of amplitude over time of the response signal is analysed for determining the position of the mover part. 
     
     
       8. The method of  claim 5 , wherein response signals of a plurality of oscillation circuits are received simultaneously for determining the position of the mover part. 
     
     
       9. The method of  claim 8 , wherein a common change of the response signals of the plurality of oscillation circuits is correlated with a change of the gap length, and a subsequent change of the response signals of the plurality of oscillation circuits is correlated with a change of position of the mover part. 
     
     
       10. The method of  claim 9 , wherein an interval of wave fronts of the response signals of the plurality of oscillation circuits is used for determining a velocity of the mover part. 
     
     
       11. An inductive sensing device for use in the method for levitation control of a linear motor of  claim 1 , the inductive sensing device comprising at least one sensing coil of an oscillating circuit, said sensing coil being arranged in a fixed spatial correlation to a mover part of the linear motor such that an opening plane of the sensing coil faces a sensor counter-surface of a stator part of the linear motor with a gap therebetween. 
     
     
       12. The inductive sensing device of  claim 11 , further comprising at least one sensing unit comprising a plurality of oscillating circuits each comprising at least one sensing coil, the sensing coils being arranged such that at least two of the sensing coils succeed each other in the moving direction of the mover part, and/or at least two of the sensing coils overlap each other in the moving direction. 
     
     
       13. The inductive sensing device of  claim 12 , wherein two of the sensing coils succeeding each other in the moving direction are displaced from each other crossways of the moving direction. 
     
     
       14. The inductive sensing device of  claim 12 , wherein the stator part at the sensor counter-surface has first regions of a first electric conductivity and/or magnetic permeability having a first length, and second regions of a second electric conductivity and/or magnetic permeability lower than the first electric conductivity and/or magnetic permeability having a second length, the first regions and second regions formed alternatingly in a moving direction of the mover part of the linear motor, and an extension of each of the sensing coils coinciding with the smallest one of the first length and the second. 
     
     
       15. An elevator system comprising:
 at least one elevator car running in an elevator shaft and movable by a linear motor; and 
 a control device for controlling the linear motor, 
 wherein the linear motor comprises a mover part fixed to the elevator car and a stator part fixed to the elevator shaft, 
 wherein the elevator car comprises an inductive sensing device comprising at least one sensing coil of an oscillating circuit, said sensing coil being arranged in a fixed spatial correlation to a mover part of the linear motor such that an opening plane of the sensing coil faces a sensor counter-surface of a stator part of the linear motor with a gap therebetween, and 
 wherein the control device is adapted to execute the steps of the method of  claim 1 . 
 
     
     
       16. A method for determining a position of a linear motor, comprising the steps:
 supplying an alternating current or alternating voltage to at least one oscillating circuit comprising at least one sensing coil arranged in a fixed spatial correlation to a mover part of the linear motor such that an opening plane of the sensing coil faces a sensor counter-surface of a stator part of the linear motor with a gap therebetween, and an oscillator parallel to the at least one sensor coil; 
 receiving a response signal from the oscillating circuit; and 
 determining a position of the linear motor based on the response signal. 
 
     
     
       17. The method of  claim 16 , wherein the oscillator is an inductance-to-digital converter having a conversion rate of 1000 ksps OF more. 
     
     
       18. The method of  claim 1 , wherein the method is executed using an inductance-to-digital converter having a conversion rate of 100,000 ksps or more. 
     
     
       19. The inductive sensing device of  claim 14 , wherein the first length is smaller than or equal to the second length. 
     
     
       20. The inductive sensing device of  claim 19 , wherein the second length is an integer multiple of the first length.